Many techniques have been used to purify and isolate liquids or to obtain concentrated pools of specific ions or molecules from a liquid mixture, such as electrodialysis, liquid chromatography, membrane filtration and ion exchange, etc. At present, a well known process is electrodeionization (EDI). We also call it CDI (continuous deionization).
The first apparatus and method for treating liquids by electrodeionization was described by Kollsman in U.S. Pat. Nos. 2,689,826 and 2,815,320. Improved and advanced electrodeionization systems have been shown in U.S. Pat. Nos. 4,925,541, 4,931,160 and 5,316,637.
The typical structure of above-mentioned electrodeionization module is like a stacked mechanical sheet type, namely ion exchange membrane, separating wall and electrodes are processed to form a rectangle, and packed in sequence, ion exchange resin is filled up, and then is pressed to form a whole with mechanical method. It is difficult to maintain and clean the apparatus, especially one has to take apart the assembly to fill or renew the ion exchange resin. In general it needs special resin like fibre shape resin; moreover the water gathering structure of depletion compartment is more complex to process and it is easy to bring about leaking in the inner part of concentration compartments and depletion compartments.